I need a way to assign and retrieve values between windows form (C#)

Question

So, I'm doing a school project atm. The application needs to be able to calculate the area of squares, circles etc.

I have one form for each figure to calculate the area off. Right now I have a "main menu" and three forms (one for each figure) and I want to be able to assign a variable LatestResult within one form and access it from the main menu form.

Note: I want to be able to do this without "loading the variable into the new form" like this: Form1 FormMainMenu = new Form1(LatestResult)

I've been trying to work with Get & Set in my Variables.cs class, but I can't seem to make it work right, if it's possible to do it with this.

EDIT: Put my code in the post

My Variables.cslooks like this:

public static string latestresult2
{
    get
    {
        return latestresult2;
    }

     set
     {
          latestresult2 = value;
     }
 }

And then I assign the value upon a button click in one form:

Variables.latestresult2 = breddeR + " * " + længdeR + " = " + resultat;

breddeR and længdeR are the int variables for my calculation and resultat is the result.

At last I try to do this in another form:

label1.Text = Variables.latestresult2;

EDIT 2:

From my MainView form

private void button1_Click(object sender, EventArgs e)
{
    Form2 FormTrekant = new Form2();
    FormTrekant.Show();
}

Answer 1

You may use the INotifyPropertyChanged interface to facilitate this. This interface works with both WinForms and WPF.

public class Form2 : Form, INotifyPropertyChanged
{
    public string latestresult2;
    public event PropertyChangedEventHandler PropertyChanged;

    public string LatestResult2
    {
        get
        {
            return latestresult2;
        }

        set
        {
            latestresult2 = value;
            this.OnPropertyChanged("LatestResult2");
        }
    }

    private void OnPropertyChanged(string propertyName)
    {
        var handler = this.PropertyChanged;
        if (handler == null)
        {
            return;
        }

        handler(this, new PropertyChangedEventArgs(propertyName));
   }
}

public class Form3 : Form, INotifyPropertyChanged
{
    public string latestResult3;
    public event PropertyChangedEventHandler PropertyChanged;

    public string LatestResult3
    {
        get
        {
            return latestresult3;
        }

        set
        {
            latestresult3 = value;
            this.OnPropertyChanged("LatestResult3");
        }
    }

    private void OnPropertyChanged(string propertyName)
    {
        var handler = this.PropertyChanged;
        if (handler == null)
        {
            return;
        }

        handler(this, new PropertyChangedEventArgs(propertyName));
   }
}

The INotifyPropertyChanged interface allows you to subscribe to another objects property changes. In the above code, the second form will raise the event when ever its LatestResult2 property has had its value changed.

Now you just have your Form1 subscribe to it.

public class MainForm : Form
{
    private Form2 secondaryForm;
    private Form3 thirdForm;

    public string LatestValue {get; set;}

    public void Form2ButtonClick() // Assume this happens in a button click event on MainWindow.
    {
        this.secondaryForm = new Form2();
        this.secondaryForm.PropertyChanged += this.LatestValueChanged;
        this.secondaryForm.Closing += this.ChildWindowClosing;
    }

    public void Form3ButtonClick() // Assume this happens in a button click event on MainWindow.
    {
        this.thirdForm = new Form3();
        this.thirdForm.PropertyChanged += this.LatestValueChanged;
        this.thirdForm.Closing += this.ChildWindowClosing;
    }

    private void LatestValueChanged(object sender, PropertyChangedEventArgs e)
    {
        // Do your update here.
        if (sender == this.secondaryForm)
        {
            this.LatestValue = this.secondaryForm.LatestValue2;
        }
        else if (sender == this.thirdForm)
        {
            this.LatestValue = this.thirdForm.LatestValue3;
        }
    }

    // Clean up our event handlers when either of the children forms close.
    private void ChildWindowClosing(object sender, ClosingWindowEventHandlerArgs args)
    {
        if (sender == this.secondaryForm)
        {
            this.secondaryForm.Closing -= this.ChildWindowClosing;
            this.secondaryForm.PropertyChanged -= this.LatestValueChanged;
        }
        else if (sender == this.thirdForm)
        {
            this.thirdForm.Closing -= this.ChildWindowClosing;
            this.thirdForm.PropertyChanged -= this.LatestValueChanged;
        }
    }
}

Your MainWindow can now react to changes within Form2, without having to pass values around. One thing to note, is that you will want to unsubscribe from the event when the Form2 is closed. Otherwise you will leak.

Answer 2

You can specify the instance of the main view to the other view. This way, you can access the properties of the main view.

Some code to explaain;

public class MainView
{
    public string LatestResult { get; set; }
}

public class ChildView
{
    private readonly MainView MainView;
    public ChildView(MainView mainView)
    {
        this.MainView = mainView;
    }
    public void Calculation()
    {
        //Some calculation
        this.MainView.LatestResult = "Some result";
    }
}

Now this code can be used like this:

var mainView = new MainView();

var childView = new ChildView(mainView);
childView.Calculation();

//mainView.LatestResult == "Some result"